The present invention relates to a receiving apparatus and a receiving method, and a program. More particularly, the invention relates to a receiving apparatus and a receiving method, and a program that can perform antenna control easily and optimally in receiving a radio wave via one of two antennas.
A conventional wireless LAN (Local Area Network) device that controls diversity antennas will be described with reference to FIG. 1.
The wireless LAN device 10 is connected to a host communication controlling unit 11 incorporated in a personal computer. The wireless LAN device 10 has an antenna 21, an antenna 22, a diversity antenna changing switch 23, a transmission/reception changing switch 24, an RF (Radio Frequency)/IF (Intermediate Frequency) device 25, a baseband processor 26, and a media access controller 27.
The diversity antenna changing switch 23 performs switching between the antenna 21 and the antenna 22 during a preamble signal period of each received packet to receive a preamble signal via each of the antennas.
The RF/IF device 25 obtains an RF signal including a component in a predetermined frequency band of the signal received by each of the antennas. In addition, the RF/IF device 25 obtains an IF level detection signal by subjecting the RF signal to amplification, frequency conversion, and band limitation, and then supplies the IF level detection signal to the baseband processor 26. The baseband processor 26 compares the IF levels (signal strengths) of the antennas with each other, and controls the diversity antenna changing switch 23 to select the antenna having the higher level. Thereby, after the preamble signal period of the received packet, data is received by the antenna selected by the diversity antenna changing switch 23.
Thus, the wireless LAN device 10 determines the signal strengths of the packet received by the two antennas to receive the packet by the antenna having the higher IF level.
Further, for example, Japanese Patent Laid-Open No. 2000-41020 discloses the provision of two sets of circuits for separating an OFDM (Orthogonal Frequency Division Multiplexing) high frequency signal into a signal of each of carrier waves forming the OFDM signal and selection by a synthesizing circuit of a signal of greater amplitude from signals output from the two sets of circuits.
However, since the wireless LAN device 10 shown in FIG. 1 checks the signal strengths of each packet received by the two antennas, a high speed switch for changing the antennas is required, and control of the switch needs to be performed steadily at high speed, thus imposing a heavy load on a control device.
Further, for example, a length of a part (length of a preamble and length of a header) other than a data part in IEEE (Institute of Electrical and Electronics Engineers) 802.11a and IEEE802.11g using OFDM modulation is 16 μs, which is very short as compared with IEEE802.11b using CCK (Complementary Code Keying) in which a length of a part (length of a preamble and length of a header) other than a data part is 192 μs. When the preamble length is short as in IEEE802.11a, it is difficult to check the levels of both antennas during the preamble signal period with the wireless LAN device 10 shown in FIG. 1 and the method disclosed in Japanese Patent Laid-Open No. 2000-41020.
Further, the wireless LAN device 10 shown in FIG. 1 and the method disclosed in Japanese Patent Laid-Open No. 2000-41020 select a signal of high reception level at all times. However, when the reception level becomes higher than a certain level, distortion may occur in a receiving circuit such as, for example, an LNA (Low Noise Amplifier) incorporated in the RF/IF device 25, so that a packet error may occur. That is, it is not necessarily desirable to select an antenna having a high reception level when a wireless LAN device at the other end of the communication is situated nearby.